Semiconductor devices are commonly found in modern electronic products. Semiconductor devices vary in the number and density of electrical components. Discrete semiconductor devices generally contain one type of electrical component, e.g., light emitting diode (LED), small signal transistor, resistor, capacitor, inductor, and power metal oxide semiconductor field effect transistor (MOSFET). Integrated semiconductor devices typically contain hundreds to millions of electrical components. Examples of integrated semiconductor devices include microcontrollers, microprocessors, charged-coupled devices (CCDs), solar cells, and digital micro-mirror devices (DMDs).
Semiconductor devices perform a wide range of functions such as signal processing, high-speed calculations, transmitting and receiving electromagnetic signals, controlling electronic devices, transforming sunlight to electricity, and creating visual projections for television displays. Semiconductor devices are found in the fields of entertainment, communications, power conversion, networks, computers, and consumer products. Semiconductor devices are also found in military applications, aviation, automotive, industrial controllers, and office equipment.
Semiconductor devices exploit the electrical properties of semiconductor materials. The atomic structure of semiconductor material allows its electrical conductivity to be manipulated by the application of an electric field or base current or through the process of doping. Doping introduces impurities into the semiconductor material to manipulate and control the conductivity of the semiconductor device.
A semiconductor device contains active and passive electrical structures. Active structures, including bipolar and field effect transistors, control the flow of electrical current. By varying levels of doping and application of an electric field or base current, the transistor either promotes or restricts the flow of electrical current. Passive structures, including resistors, capacitors, and inductors, create a relationship between voltage and current necessary to perform a variety of electrical functions. The passive and active structures are electrically connected to form circuits, which enable the semiconductor device to perform high-speed calculations and other useful functions.
Semiconductor devices are generally manufactured using two complex manufacturing processes, i.e., front-end manufacturing, and back-end manufacturing, each involving potentially hundreds of steps. Front-end manufacturing involves the formation of a plurality of die on the surface of a semiconductor wafer. Each die is typically identical and contains circuits formed by electrically connecting active and passive components. Back-end manufacturing involves singulating individual die from the finished wafer and packaging the die to provide structural support and environmental isolation.
One goal of semiconductor manufacturing is to produce smaller semiconductor devices. Smaller devices typically consume less power, have higher performance, and can be produced more efficiently. In addition, smaller semiconductor devices have a smaller footprint, which is desirable for smaller end products. A smaller die size may be achieved by improvements in the front-end process resulting in die with smaller, higher density active and passive components. Back-end processes may result in semiconductor device packages with a smaller footprint by improvements in electrical interconnection and packaging materials.
FIGS. 1 and 2 illustrate a cross-sectional view and top view of a portion of flipchip type semiconductor die 10 and interconnects or bumps 12 metallurgically and electrically connected between bump pads 18 as formed on semiconductor die 10 and trace lines 20 and 22 as formed on substrate 30. Trace line 22 is routed between traces lines 20 and bumps 12 on substrate 30. Trace lines 20 and 22 are electrical signal conductors with optional bump pads for mating to bumps 12-14. Solder mask 26 overlays trace lines 20 and 22. Solder mask or registration openings (SRO) 28 are formed over substrate 30 to expose trace lines 20 and 22. SRO 28 confines the conductive bump material on the bump pads of trace lines 20 and 22 during reflow and prevents the molten bump material from leaching onto the trace lines, which can cause electrical shorts to adjacent structures. SRO 28 is made larger than the trace line or bump pad. SRO 28 is typically circular in shape and made as small as possible to reduce the pitch of trace lines 20 and 22 and increase routing density.
In typical design rules, the minimum escape pitch of trace line 30 is defined by P=(1.1D+W)/2+L, where D is bump base diameter, W is trace line width, and L is the ligament separation between SRO and adjacent structures. Using a solder registration design rule of ±30 micrometers (μm), D of 100 μm, W of 20 μm, and L of 30 μm, the minimum escape pitch of trace lines 30-34 is (1.1*100+20)/2+30=95 μm. SRO 28 around the bump pads limits the escape pitch and routing density of the semiconductor die.